The present invention relates to a new catalyst composition and a process for preparing linear, isotactic polymers, wherein the isotacticity of the linear polymers due to a statistic distribution of stereoscopic errors in the polymer chain, being within the range of from 25 to 60% of pentad concentration.
For a long time, isotactic polymers have been of interest as plastic materials for manufacturing articles of relatively good deformation resistance, such as sheathings of household appliances. In general, such isotactic polymers with propylene as monomer are highly crystalline nature and, therefore, are relatively hard with little or no impact resistance such that they are useful only in applications in which hardness or low impact resistance is desirable.
Most recently, various attempts have been made, aiming at preparing polypropylene with elastic characteristics. EP 0 707 016 A1 specifies a catalyst composition and a process for preparing polyolefins. The catalysts specified in EP 0 707 016 A1 are, in substance, made up of a metallocene compound having an indene ring and a fluorene ring which are bridged via C, Si or Ge. In case of the metallocene compound, it is essential that, in the indene ring system, at least the residue denoted with R4 not be hydrogen. When that residue R4 is hydrogen, the effects will not be attained. The polymers specified in EP 0 707 016 A1 and prepared with metallocenes, especially the polypropylene prepared with those metallocenes, however, have shown unsatisfactory characteristics in regard of the elastic behavior.
It is the object of the present invention to find a new catalyst and a process for making polymers from olefinically unsaturated compounds, which have not only thermoplastic characteristics, but also thermoplastic-elastic characteristics, thus making the polymers useful for many applications.